FixedSizeAggregateInGallery

Changed AggregateInGallery to never process more than 1000 records at a time. Currently, 1000 is hard-coded

NOTE: On average, 1000 records take 5 seconds to execute. 10000 could not be completed in the default 30 seconds timeout, so, sticking with 1000

TODO: Make offset a parameter of the job instead of hard-coding it
Need to guard against the offset addition leading to a key that doesn't actually exist in the table.

I would suggest:

``` sql
SET DownloadStatsLastAggregatedId = (SELECT MAX([Key]) FROM PackageStatistics WHERE [Key] <= @LatestGallerySettingPlusOffset)
```

If you do that, while also guarding to make sure @LatestGallerySettingPlusOffset is never null, then you should be okay.